The present invention relates to an improved industrial fabric which is particularly suitable for papermaking and related filtration applications to aid in forming, dewatering and conveying a web through a papermaking or like machine. The requirements and desirable characteristics of papermaker's fabrics vary depending on the particular section of the papermaking machine where the fabric is intended to be used, and the paper product being manufactured. The vast majority of these fabrics are of woven construction. Many types are known in the art, including those with single layer, double or triple layer construction. These fabrics are either flat or endlessly woven according to techniques well known in the art and are seamed to facilitate their installation on the papermaking machine.
Papermaker's fabrics must generally satisfy a number of physical requirements simultaneously: they must be dimensionally stable and have a reasonably high tensile strength, so as to resist the stresses to which they are exposed; they must be resistant to high temperatures and compressive loading; and they must be reasonably resistant to the effects of abrasion caused by their movement over bearing surfaces in the machine. Other requirements are known. To satisfy at least some of these requirements, manufacturers of papermaker's fabrics have developed various weave designs and fabric constructions which allow the properties of one or both fabric surfaces to be customized for end use conditions. One method of doing this is to cause the yarns in either, or both, the warp and weft systems to be stacked so that the individual yarns of each system are in vertical alignment with each other.
Woven industrial fabrics comprised of stacked warp and/or weft yarns are known in the art. See, for example, U.S. Pat. Nos. 5,066,532 and 5,857,497 to Gaisser, U.S. Pat. Nos. 5,167,261, 5,092,373 and 5,230,371 to Lee, U.S. Pat. No. 6,158,478 to Crosby et al., U.S. Pat. No. 5,503,196 to Josef et al., and U.S. Pat. No. 5,503,196 to Kositzke. Others are known and used. The known fabrics comprised of stacked warp and/or weft yarns are at least double layer structures, meaning they have at least two systems of either, or both, warp or weft yarns. In these known fabrics, at least a portion of either the warp yarns, or the weft yarns, or both, from one yarn system are arranged in the weave pattern so as to be in a vertically stacked relationship over the corresponding yarns in the second yarn system in the woven fabric structure.
In all of the known fabrics in which each of at least a portion of the component yarns of one system are vertically stacked over a corresponding yarn of a second system to form e.g., a pair, the component yarns of a pair are not in intimate contact over their entire path length through the fabric. There is always at least one intervening yarn located between a stacked pair in the weave repeat. This is because the weave patterns of at least some of these prior art fabrics are designed so as to stabilise the stacked yarns in their vertical orientation so that they are maintained in this position one above the other.
The prior art fabrics wherein the warp and/or weft yarns are vertically stacked provide numerous advantages over other fabrics in which at least a portion of the component yarns are not stacked. For example, the weave paths of stacked yarns can be arranged so that one yarn system forms a portion of only one fabric surface, while the other yarn system forms a portion of the opposite fabric surface. This feature can be utilised to locate temperature resistant, or abrasion resistant, materials on one surface of the fabric so as to increase its operational life. In certain weave constructions, fabrics with stacked yarn systems can also provide improved seam strength and reduced seam marking when compared to fabrics where the yarn systems are not stacked. In addition, it is also possible to obtain relatively high air permeability and open area in a stable fabric structure, increased fabric surface area contact and smoothness when compared to non-stacked designs, and high fabric warp fill. Thus, it is recognised in the art that fabrics having stacked yarn systems can provide numerous advantages, depending on their intended end use, when compared to fabrics in which the component yarns are arranged in a non-stacked relation.
However, it has now been recognised that these known fabrics suffer from several limitations due to the manner in which the component yarns are arranged. First, the number of possible weave designs available which will allow one of the component yarns of one yarn system to be located predominantly on one fabric surface, while causing the component yarns of the second yarn system to be located predominantly on the opposed fabric surface, is somewhat limited. Second, the number of seam designs available for use in these prior art fabric structures to create a high strength, low marking seam to join the opposed fabric ends is also limited. Third, it is not possible in a single layer fabric (one having a single system of warp and weft yarns) to provide differing yarn materials on each of the fabric surfaces without post-treating the fabric (e.g. by applying a coating or an additional layer of material such as a nonwoven batt or film to one surface).
It would therefore be desirable if a woven industrial fabric of any chosen design can be provided wherein the physical characteristics of the two opposed fabric surfaces can be different, the seam has reduced potential to mark the sheet and is of high strength, the seaming loops can be orthogonal to the plane of the fabric, and which also offers improved economy of manufacture.
Accordingly, the present invention seeks to provide an industrial fabric, in particular a papermaker's fabric or filtration fabric, whose construction is intended at least to ameliorate the aforementioned deficiencies of the prior art.
It has now been discovered that it is possible to weave, or assemble, an industrial fabric using a plurality of yarn assemblies. The yarn assemblies may be used as either, or both, the warp and weft systems in the fabric. Each yarn assembly is comprised of at least two yarn members which are arranged so as to be in generally continuous intimate contact over their entire weave path through the industrial fabric with no yarns from another system intervening between any yarn members in the fabric.